In the filtration of air to purify it, it is known to introduce the air into essentially cylindrical hoses manufactured from filtering material, so as to make the air pass through the material and arrest impurities inside the hose.
When such hoses have to be of considerable length, and/or when the pressure of the air to be filtered is weak, or when the current of air or some other gas has to be inverted so as to clean the filtering material, it is necessary to stiffen such hoses at regular intervals with braces to prevent them from retracting or collapsing upon themselves.
A cross-section of a known reinforced filtering tube or hose is shown in FIG. 1. Filtering material (1) of which the hose is made is surrounded by a band (2) of an essentially rigid stiffener, made out of metal or plastic, for example, and a covering band (3) of material (for example, of the same material as the filtering material) is placed so as to cover band (2), and is attached to the filter material (1) on either sides of the band (2), usually by a pair of sewn seams (4,4') on both sides. A similar structure is also known in which band (2) and covering band (3) are situated inside the hose.
This hose has a major drawback. The presence of numerous stitches on both sides of band (2) causes local damage to the filtering material (1), since the thread of the seam stitching passes through this filtering material at regular intervals. More precisely, those stitches inevitably form a large number of small holes via which the dust and other impurities can get through to the filter. Thus, the quality of filtration is substantially reduced.
The present invention eliminates the disadvantage of previous technology, and provides a filtering hose or tube with stiffening bands in which securing the bands in their place does not cause any deterioration to the filtering quality.